The present description generally relates to a supercharger for an internal combustion engine, and more particularly relates to a method of diagnosing a supercharger which is driven by a motor such as an electric motor.
Conventionally, a mechanical supercharger and a turbocharger are known to boost intake air to the engine. The mechanical supercharger is driven by the engine crankshaft. The turbocharger is driven by the engine exhaust gas. Therefore, the engine speed and how it is related to engine flow influence supercharging efficiencies. In particular, those superchargers may boost less air in the lower engine speed range where engine flow may be limited.
To improve the supercharging efficiencies in the lower speed range, there is known and presented, for example in European Patent EP1342895B1, an electrically driven compressor. The electric compressor is arranged in the engine intake system upstream of the turbocharger compressor and boosts the intake air in addition to the turbocharger.
The '895 patent also shows a method of diagnosing the electric compressor operation by comparing boosting power output from and electric power input to the electric compressor. These parameters are derived using an engine system model. As a result, the method of the '895 patent can diagnose a degradation of the supercharger operation during engine operation. However, conditions affecting the parameters may fluctuate during the engine operation, thereby reducing the diagnostic confidence level. For example, there is a fluctuation of the intake air pressure as the engine is cyclically inducting the air. In some cases, it is possible for the intake air pressure fluctuation to overcome a change of the pressure of the air boosted by the electric compressor.
Therefore, there is room to improve the accuracy of the diagnosing the supercharger operation.